Zirconium-based alloys have been used for a long time in components for nuclear reactors both of the boiling-water type and the pressurized-water type, because of the low absorption cross section of the zirconium for neutrons and their good corrosion resistance to water and water steam under the operating conditions prevailing in the reactor core. The alloys which are most used are zirconium-tin alloys, especially the zirconium-based alloys known under the trade names Zircaloy 2 and Zircaloy 4, the contents of alloying materials of which are within the limits 1.2-1.7 percent by weight for tin, 0.07-0.24 per cent by weight for iron, 0.05-0.15 per cent by weight for chromium, 0-0.08 per cent by weight for nickel, 0.09-0.16 per cent by weight for oxygen, the balance being zirconium and impurities normally occurring in reactor grade sponge zirconium. Zircaloy 2 contains 1.2-1.7 per cent by weight tin, 0.07-0.20 per cent by weight iron, 0.05-0.15 per cent by weight chromium, 0.03-0.08 per cent by weight nickel and 0.09-0.16 per cent by weight oxygen. Zircaloy 4 contains 1.2-1.7 per cent by weight tin, 0.18-0.24 per cent by weight iron, 0.07-0.13 per cent by weight chromium and 0.09-0.16 per cent by weight oxygen. The impurities occurring in reactor grade sponge zirconium consist of the following substances in the contents stated: aluminium 75 ppm or less, boron 0.4 ppm or less, cadmium 0.4 ppm or less, carbon 270 ppm or less, chromium 200 ppm or less, cobalt 20 ppm or less, copper 50 ppm or less, hafnium 100 ppm or less, hydrogen 25 ppm or less, iron 1500 ppm or less, magnesium 20 ppm or less, manganese 50 ppm or less, molybdenum 50 ppm or less, nickel 70 ppm or less, niobium 100 ppm or less, nitrogen 80 ppm or less, oxygen 200-1200 ppm, silicon 120 ppm or less, tin 50 ppm or less, tungsten 100 ppm or less, titanium 50 ppm or less, and uranium 3.5 ppm or less.
Of the above-mentioned alloys, above all Zircaloy 2 has become extensively used because of its good resistance to corrosion by water and water steam. Zircaloy 2 is thus a conventional and well-tested material which fulfills the existing specifications for the applications in questions. Zircaloy 4 does not possess the same good resistance to corrosion by water and water steam as Zircaloy 2 but has a greater resistance to hydrogen absorption during operation of the reactor. Hydrogen absorption leads to embrittlement of the material.